An ever-increasing number of relatively inexpensive, low power wireless data communication services, networks and devices have been made available over the past number of years, promising near wire speed transmission and reliability. Various wireless technology is described in detail in the 802 IEEE Standards, including for example, the IEEE Standard 802.11a (1999) and its updates and amendments, the IEEE Standard 802.11n, and the IEEE draft standards 802.15.3, and 802.15.3c now in the process of being finalized, all of which are collectively incorporated herein fully by reference.
As one example, a type of a wireless network known as a wireless personal area network (WPAN) involves the interconnection of devices that are typically, but not necessarily, physically located closer together than wireless local area networks (WLANs) such as WLANs that conform to the IEEE Standard 802.11a or the IEEE Standard 802.11n. Recently, the interest and demand for particularly high data rates (e.g., in excess of 1 Gbps) in such networks has significantly increased. One approach to realizing high data rates in a WPAN is to use hundreds of MHz, or even several GHz, of bandwidth. For example, the unlicensed 60 GHz band provides one such possible range of operation.
In general, transmission systems compliant with the IEEE 802.15.3c or future IEEE 802.11ad standards support one or both of a Single Carrier (SC) mode of operation and an Orthogonal Frequency Division Multiplexing (OFDM) mode of operation to achieve higher data transmission rates. For example, a simple, low-power handheld device can operate only in the SC mode, a more complex device that supports a longer range of operation can operate only in the OFDM mode, and some dual-mode devices may switch between SC and OFDM modes. Additionally, devices operating in such systems can support a control mode of operation at the physical layer of the protocol stack, referred to herein as “control PHY.” Generally speaking, control PHY of a transmission system corresponds to the lowest data rate supported by each of the devices operating in the transmission system. Devices may transmit and receive control PHY frames to communicate basic control information such as beacon data or beamforming data, for example.
By transmitting beacon data, network devices such as piconet central points (PCPs) announce the presence of the network to devices not yet associated with the network. Devices can utilize the beacon data to become associated with the PCP.
As is known, antennas and, accordingly, associated effective wireless channels are highly directional at frequencies near or above 60 GHz. When multiple antennas are available at a transmitter, a receiver, or both, it is therefore important to apply efficient beam patterns using the antennas to better exploit spatial selectivity of the corresponding wireless channel. Generally speaking, beamforming or beamsteering creates a spatial gain pattern having one or more high gain lobes or beams (as compared to the gain obtained by an omni-directional antenna) in one or more particular directions, with reduced gain in other directions. If the gain pattern for multiple transmit antennas, for example, is configured to produce a high gain lobe in the direction of a receiver, better transmission reliability can be obtained over that obtained with an omni-directional transmission.
U.S. patent application Ser. No. 12/548,393, filed on Aug. 26, 2009, and entitled “Beamforming by Sector Sweeping,” and U.S. Provisional Patent Application No. 61/091,914 entitled “Beamforming by Sector Sweeping,” filed Aug. 26, 2008, are both expressly incorporated by reference herein in their entireties. These applications are generally related to a beamforming technique referred to as “beamforming by sector sweeping.” In one implementation of beamforming by sector sweeping for determining a transmit beamforming pattern to be applied by a first device when transmitting data to a second device, the first device transmits a plurality of training packets to the second device, where the first device applies a different beamforming pattern when transmitting each training packet. The second device generally determines which of the training packets had the highest quality (e.g., had the highest signal-to-noise ratio (SNR), the lowest bit error rate (BER), etc.) and notifies the first device. The first device can then utilize the transmit beamforming pattern that yielded the highest quality packet. Similarly, to determine a receive beamforming pattern to be applied by the first device when receiving data from the second device, the second device transmits a plurality of training packets to the first device, and the first device applies a different beamforming pattern when receiving each training packet. The first device generally determines which of the training packets had the highest quality, and can then utilize the receive beamforming pattern that yielded the highest quality packet.
Network devices can apply the techniques described above during dedicated timeslots to process real-time requests, or during beacon or association stages. Of course, communicating beacon and/or beamforming data during certain time intervals prevents network devices from transmitting useful data during these intervals. The transmission of beacons and beamforming data accordingly contributes to an overhead that reduces the effective throughput of the wireless channel. Further, the overhead increases with the number of sectors used in sector sweeping.